Existing roll type material feeding apparatus utilize a pair of rolls for gripping and intermittently feeding a workpiece between the rolls. Many such roll feeding apparatus utilize a high performance servo motor for rotating the rolls. An example of such an apparatus is represented by U.S. Pat. No. 5,808,465 issued to Gentile et. al. in 1998, the disclosure of which is incorporated by reference. The apparatus of U.S. Pat. No. 5,808,465 utilizes a high performance servo motor for rotating a pair of rolls for intermittently feeding a strip-like sheet material workpiece.
A first limitation of existing roll type material feeding apparatus results when the length of the rolls must be increased in order to accommodate wider strip-like workpieces. As roll width increases, roll inertia increases, thereby resulting in decreased performance levels or alternatively more powerful motors are required. In order to meet the demand for more powerful motors, two options are available. Increase the motor diameter, or increase the motor length. If the motor diameter is increased, the resulting motor will indeed be capable of producing more torque, however the inertia of the motor is increased, and the resulting performance gain of the overall system is small. If the motor length is increased, there becomes a practical limitation to the length increase due to constraints in winding the motor coils on motors with a high length-to-diameter ratio.
A second limitation of existing roll type material feeding apparatus results when the length of the rolls are increased in order to accommodate wider strip-like workpieces. As the roll width increases, the torsional stiffness of the rolls is decreased. As the torsional stiffness of the apparatus is decreased the accuracy of the feed apparatus is decreased due to wind-up or twist of the roll between the high performance servo motor that is driving the roll and the workpiece held between the rolls. Furthermore, the rate of intermittent feeding of the workpiece is reduced. The rate at which intermittent feeding can occur is limited by the ability of the high performance servo motor to controllably start and stop the movement of the rolls and subsequently the workpiece. The controllability of a high performance servo motor is in direct correlation to the stiffness of the system being controlled, in this case the rolls of the feeding apparatus.
Accordingly, the present invention provides an electric servo motor driven roll type feeding apparatus capable of high rates of intermittent feeding of a wide strip-like workpiece which utilizes low inertia motors with improved length-to-diameter ratios for improved manufacturability.
The present invention provides an electric servo motor driven roll type feeding apparatus capable of high rates of intermittent feeding of a wide strip-like workpiece with improved torsional stiffness and subsequently improved accuracy and controllability.